Column-switching procedure

Veuthey, J. L., Souverain, S., and Rudaz, S. (2004). Column-switching procedures for the fast analysis of drugs in biologic samples. I her. Drug. Monit. 26 161-166. 

HPLC with column switching and mass spectrometry was applied to the online determination and resolution of the enantiomers of donepezil HC1 in plasma [38]. This system employs two avidin columns and fast atom bombardment-mass spectrometry (FAB-MS). A plasma sample was injected directly into an avidin trapping column (10 mm x 4.0 mm i.d.). The plasma protein was washed out from the trapping column immediately while donepezil HC1 was retained. After the column-switching procedure, donepezil HC1 was separated enantioselectivity in an avidin analytical column. The separated donepezil HC1 enantiomers were specifically detected by FAB-MS without interference from metabolites of donepezil HC1 and plasma constituents. The limit of quantification for each enantiomer of donepezil HC1 in plasma was 1.0 ng/ml and the intra-and inter-assay RSDs for the method were less than 5.2%. The assay was validated for enantioselective pharmacokinetic studies in the dog. 

A publication describes a column switching procedure for an imatinib assay, involving a C8 extraction column, followed after activation of the switching valve by the back-flushing of imatinib onto a C18 analytical column [107], The run time was 10 min. The other published methods use HPLC with C18 columns with analytical times of 2 min [106], 3 min [103], 6 min [110], 10 min [107], 14 min [108], and 20 min [109], C8 columns were used by two groups with analytical times varying between 2.5 min [104] and as much as 40 min [105],... 

DIN 51448-1-97. Testing of liquid petroleum hydrocarbons. Determination of hydrocarbon types. Part 1 Gas chromatographic analysis by column switching procedure. 

For solid-phase extraction, the offline procedure, based on sample pretreatment on disposable SPE cartridges, and a totally automated online procedure, based on column switching, have been developed. The column switching procedure involves the use of a polystyrene-divinylbenzene column for sample concentration and cleanup. 

Ll. Buglass, A. J. and S. H. Lee. 2001. Sequential analysis of malic acid and both enantiomers of lactic acid in wine using a high-performance liquid chromatographic column-switching procedure./. Chromatogr. Sci. 39 453-458. 

M. Tanaka and H. Yamazaki, Dkect detemination of pantoprazole enantiomers in human serum by reversed-phase liigh peifomance liquid chi omatography using a cellulose-based cliiral stationaiy phase and column-switching system as a sample cleanup procedure , Aim/. Chem. 68 1513-1516(1996). 

A procedure for determination of lipid hydroperoxides in human plasma is based on kinetic measurement of the CL of luminol (124) with hemin (75a) catalysis . CLD of microperoxidase-catalyzed oxidation of luminol (124) or isoluminol (190) was applied to detection and determination of amino acid hydroperoxides after exposure to UV and y-irradiation A method for determination of hydroperoxides in the phospholipids of cultured cells uses isoluminol (190) and microperoxidase as catalyst " . Simultaneous determination of phosphatidylcholine hydroperoxides and cholesteryl ester hydroperoxides in human serum is carried out by quantitative extraction of the lipids, HPLC separation by column switching and CLD using isoluminol (190) with microperoxidase catalysis . ... 

Using immobilized -glucuronidase reactors, estriol and estradiol glucuronides have been determined in urine by a column-switching technique (270, 271). Both glucuronides were hydrolyzed by the immobilized enzyme at pH 7. The steroid mixture was subsequently separated by gradient elution on a reversed-phase column, to be finally detected by UV absorbance at 280 nm. In this procedure, the activity of enzyme did not alter even after 150 h continuous run and exposure to a mobile phase containing 10% methanol. When a separate reversed-phase precolumn was inserted in the LC system, additional sample purification and shorter analysis time could be attained (272). 

Another exciting development in multidimensional separation involves coupling of LC to GC or even to CE. In these coupling systems, LC can play a role as a high-resolution procedure for preliminary separation and/or trace enrichment. LC-GC can thereby be carried out in the column-switching and in the precolumn-analytical column mode. Although on-line LC-GC has not yet advanced widely into routine analysis, this powerful technique holds promise for the future. 

Higher-specificity techniques such as immunoaffinity chromatography have been also found widespread acceptance for the determination of chloramphenicol residues in edible animal products. The first pertinent reports concerned the determination of chloramphenicol residues in swine muscle (60) and milk and eggs (21). Alternative immunoaffinity chromatography procedures were suggested later for exiraction/preconcentration of chloramphenicol residues from swine tissues (50), or for online immunoaffinity extraction for the determination of chloramphenicol in milk and swine muscle by an automated column-switching system (22). 

To eliminate or reduce interference and concentrate the analyte(s), the primary sample extract can further be subjected to various types of cleanup procedures including liquid-liquid partitioning, solid-phase extraction, immunoaffmity chromatography, and column-switching techniques (Table 29.17). In some instances, more than one of these procedures may be used in combination to enhance the cleanup efficiency. 

Tuned output control signals to peripheral and ancillary devices such as sample valves, column switching valves, and other external functions which are part of the automated procedure. 

---